1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly, to a semiconductor device capable of reducing electromigration occurring in multilevel interconnections of a high-speed integrated circuit that has a small-sized feature according to submicron design rules, and a method of manufacturing the same.
2. Description of the Related Art
As semiconductor devices are becoming more highly integrated, there is an increase in a need for multilevel interconnections. In the event that a multilevel interconnection structure is adopted in a highly integrated semiconductor memory device, thick interlayer insulating films are interposed between interconnections in order to minimize parasitic capacitance between the interconnections. As a result, in the multilevel interconnections having such thick interlayer insulating films, contacts or vias are formed to have a large aspect ratio for electrically connecting interconnection layers that are formed to have feature sizes according to submicron design rules and that are placed above and below the interlayer insulating films.
There are means by which the resistivity of a conductive pattern can be reduced in order to increase a control speed in a highly integrated semiconductor device having multilevel interconnections. In the past, a semiconductor device was manufactured mainly using aluminum for forming multilevel interconnection vias because aluminum is comparatively inexpensive, has a low resistivity, and can be easily etched. However, in this case, as the size of holes for forming vias became scaled-down to a submicron level, step coverage became inadequate using aluminum. To solve these problems, a metal interconnection layer can be formed of aluminum, and a via, which electrically connects metal interconnection layers placed in different levels, can be formed of tungsten w which is deposited by a chemical vapor deposition (CVD) method. However, in this case, some problems may occur. That is, electromigration occurs in an aluminum interconnection layer which is adjacent to the vias made of tungsten. Electromigration is a phenomenon whereby conductive ions such as aluminum ions move in the direction of electric current flow. Due to electromigration, a void is formed on an aluminum interconnection layer which is adjacent to the via and has a low electric potential. As the size of the void is increased, the interconnections are eventually disconnected. Further, when the void is formed on one end of the via, an electric current flowing through the aluminum interconnection layer is increased or the operational temperature of the semiconductor device is raised. In view of this, there is a higher probability that interconnections are disconnected, and thus, the semiconductor device malfunctions. Also, a contraction in the width of an interconnection results in an increase in the amount of electric current flowing through the interconnection, and electromigration is thus worsened, thereby increasing the likelihood of disconnecting the interconnections.